The present invention relates generally to label applicators, and is particularly concerned with a vacuum or suction applicator for receiving pressure-sensitive labels peeled from a backing strip and for applying the labels to a desired surface.
Various types of devices employing positive or negative air pressure, or both, have been proposed for use in applying adhesive-backed labels to cartons, bottles, and similar articles. One such device, employing both positive and negative pressure, consists of a hollow enclosure or housing having one wall formed with openings therein to serve as a label retaining grid. The interior of the enclosure is partially evacuated by means of an exhaust fan or other source of vacuum, causing the label to adhere to the grid by virtue of ambient air pressure. When it is desired to apply the label to an article surface, a short burst of compressed air is applied through selected portions of the grid in order to propel the label toward the article surface. The negative pressure within the enclosure is generally applied continuously, rather than intermittently, but the intermittent bursts of compressed air that are applied to the label through the selected grid openings are of sufficient force to overcome the adhesion of the label to the grid. This results in a somewhat simplified structure since it is not necessary to switch off the source of vacuum each time that a label is applied.
In one arrangement, the burst of compressed air is supplied through a plurality of flexible tubes connected to selected openings in the grid, these openings being selected to correspond generally with the shape or outline of the label to be applied. The remaining openings are left open to communicate with the interior of the enclosure, in order to provide the vacuum or suction which is necessary to adhere the label to the grid.
A label applicator of the type just described may be used to apply pressure-sensitive labels which have been peeled from a continuous backing strip by means of a stripper or peeler device located adjacent to the applicator. As the label is peeled from the backing strip, it moves across the face of the applicator grid and is held thereon with its adhesive side facing outwardly. As will be readily apparent, the degree of friction between the label and the applicator grid will increase progressively as more of the label is delivered to the applicator. This friction will exert a rearward force on the label tending to oppose the forward force exerted by the motion of the backing strip across the stripper edge. The combined effect of the forward force exerted on the label at the stripper edge, and the opposing force exerted on the label by frictional contact with the applicator grid, is to exert a buckling force on the label that may cause it to become wrinkled or bunched as it travels over the applicator grid. This condition must be avoided since the wrinkling or bunching will prevent the labels from being properly applied to the articles, and can result in jamming of the label applicator and feed mechanisms.
In order to reduce the friction between the label and the applicator grid, it has been proposed to form the grid with a plurality of parallel, spaced-apart ribs extending in the direction of label movement. The recessed spaces between adjacent ribs contain rows of holes communicating with the interior of the enclosure, or, in the case of certain holes, with the compressed air source. This arrangement has the advantage that the ribs provide a reduced area of contact between the label and the applicator grid, thereby reducing friction. In addition, since the holes are recessed away from the rib surfaces, the label edges cannot become caught on the edges of the holes.
Unfortunately, the use of parallel ribs on the surface of the applicator grid has not provided a complete solution to the problem of label wrinkling or bunching caused by excessive friction. As the length of the label is increased, the amount of friction between the label and the applicator grid increases, and furthermore, the resistance of the label to buckling decreases because of the change in the aspect ratio of the label (i.e., the relationship between its width and its length). As a result of these two factors, a limit on the maximum length of the label is quickly reached even if measures are taken to reduce friction somewhat. The thickness and stiffness of the label material will obviously have an important bearing on its resistance by buckling, and, in theory at least, it is possible to avoid the problem by employing a more rigid label material when longer labels are to be applied. In practice, however, it is desirable for reasons of economy and convenience to be able to use conventional types of label stock without regard to the size of the labels to be applied. Also, the operation of the label feeding and handling apparatus may impose certain constraints on the thickness or rigidity of the label stock, and these constraints may not be compatible with the requirements of the label applicator.